1. Field of the Invention
The present invention relates to a processing apparatus for emphasizing the edges of a video signal and, more particularly, to a processing apparatus for emphasizing the edges of a video signal to sharpen the contours within a picture produced thereby.
2. Description of the Prior Art
In the imaging art, it is a common practice to feed a television (TV) signal or like video signal to a TV receiver and other output devices after applying non-linear correction such as gamma correction to the video signal. In this instance, both highlight and shadow portions of a gamma-corrected video signal are processed for edge emphasis and, then, subjected to reverse gamma correction to produce a final picture. A problem with a prior art edge emphasizing system is that it excessively emphasizes edges on the highlight side of a picture while not sufficiently emphasizing them on the shadow side, as shown in FIG. 3 of the drawings.
Such uneven edge emphasis stems from the fact that because gamma correction and other kinds of non-linear correction are generally implemented with compansion processing: comparison processing applies the same degree of edge emphasis to both the highlight side and the shadow side of a video signal at the companded level and thus causes an edge component to appear enlarged on the highlight side and reduced on the shadow side in the eventual reverse gamma-corrected picture.